Field of the Invention
The invention relates to processes for the recovery and treatment of coal materials and, more particularly, to processes for treatment of reclaimed waste coal.
Description of Related Art
Fine by-products of coal production and preparation have been generally disposed of into waste coal ponds. These waste coal deposits are potentially useful fuels. However, because they are presently stored in coal ponds they are generally useless in their current state.
Over time, private industry and the public sector have found that there may be benefits for which to remediate these waste coal ponds. One such benefit, for example, would be to remediate a waste coal pond in order to overcome a specific environmental and/or safety challenge created by the waste coal pond such as, for example, pond failure. Accordingly, solutions to accomplish these objectives have been suggested. It has not only become possible, but desirable to develop processes and equipment for the reclamation of land and fuel that were previously useless. Further, these reclamation projects and processes that have been developed have proved to be useful tools in obtaining beneficial fuels while accomplishing environmental goals encouraged and/or mandated by the presiding governmental authorities.
A waste coal pond may be mined via dredging and the recovered materials transported to a processing plant. One problem with dredging has been that the pond from which the materials are to be recovered must be flooded. Such flooding may destabilize a previously drained waste coal pond or create new seepage problems. Also, dredging normally produces a low density slurry containing insufficient coal solids such that more slurry volume must be obtained. Handling this higher volume of material is costly due to the addition of larger sumps, pumps, piping, etc., not to mention the additional downstream equipment necessary for separating out the unwanted materials recovered. Further, with dredging, the use of the same pond for disposal of tailings is prevented and ice formation is continually a problem during the winter months.
The drawbacks of mobile equipment mining are somewhat opposed to those of dredging. In particular, the waste coal ponds cannot be mined where they are soft or flooded. Further, hauling the mined material to the processing plant can prove expensive, particularly with the escalating prices of fossil fuels. In addition, vibration of the waste coal materials during transport tends to liquefy the entire mass. This results in making discharge of the waste coal material from the hauling vehicle very difficult and stockpiling of the waste coal material recovered nearly impossible.
Once the waste coal is harvested, it is first sorted and classified. A small portion of the waste coal may contain larger particulates of uncontaminated, or useful, coal that are then reclaimed immediately in the first step. However, smaller particulates are passed into a large multi-stage treatment process to reclaim finer particles of coal that may or may not have other sediments attached and coexist with contaminating mineral matter particles. Accordingly, the waste coal must be processed to separate it into its component parts in order to harvest the useful coal within the slurry.
In reclamation operations, problems unique to the size of waste coal materials obtained for these processes confound their purpose. For example, many of the separated finer particulates of waste coal exist in a clay-rich environment. This is a problem in that with decreasing particle size there is an exponential increase in the number of particles and subsequent surface onto which clay or other materials may attach and, therefore, cover the useful coal. In order to obtain useful coal from waste coal, these contaminates must be stripped from the useful coal so that a market-required BTU value and ash content can be achieved.
Numerous mechanical and chemical treatments must be performed in the processing plant to separate out the useful coal particulates from the remainder of the materials transported into the processing plant as waste coal. Due to contaminants surrounding the waste coal, excess water may be carried by these contaminants that adhere to the waste coal. Processes are generally known for the breaking up of the waste coal and contaminant agglomerates into their component parts by shearing and dispersion using large tanks with mechanical apparatuses and chemical additives to effectuate the necessary levels of separation. These processing methods and associated equipment have been developed to accomplish agglomerate dispersion once the waste coal has been harvested from the waste coal pond, although at a significant cost. More specifically, such processes can be time consuming and costly, requiring large energy costs, equipment costs, maintenance costs and chemical treatment costs, etc. However, currently these or similar costly agglomerate dispersion processes are necessary in order to facilitate the obtainment of useful coal products from the harvested waste coal which significantly increase labor and material costs associated with waste coal recovery operations.